Aristotle · a new plain-English translation from the original language
1| Or rather, smelling is perceiving, and the air, once affected, quickly becomes perceptible. That there is no perception other than the five (I mean these: sight, hearing, smell, taste, touch) one might be persuaded of from the following. For if touch is the perception of everything of which there is perception, and we now have perception (for all the affections of the tangible qua tangible are perceptible to us by touch), then it is necessary, if any perception is lacking to us, that some sense-organ be lacking to us as well. And whatever things we perceive by touching them ourselves are perceptible by touch, which we happen to have; but whatever things we perceive through intermediaries, and not by touching the things themselves, we perceive by the simple bodies, I mean for example air and water. And the situation is this: if a number of perceptibles that differ in kind from one another are perceived through one and the same medium, then whoever has that sense-organ must be capable of perceiving both; for example, if the sense-organ is made of air, and air is a medium of both sound and color. But if several media serve the same perceptible, for instance color has both air and water as media (for both are transparent), then whoever has only one of these will still perceive both. Now of the simple bodies, there are sense-organs from only two of these, from air and from water; for the pupil is of water, hearing is of air, and smell is of one or the other of these.
2| Fire either belongs to none of the senses or is common to all of them, for nothing is capable of perceiving without heat. Earth either belongs to none, or is mixed in a particular way most of all in touch. Hence it would remain that there is no sense-organ apart from water and air. And some animals now have just these. Therefore all the senses belong to animals that are not incomplete or maimed; for even the mole is seen to have eyes under its skin. So that, unless there is some other body, and some affection belonging to none of the bodies here, no sense could be lacking. But moreover, there cannot be any special sense-organ for the common perceptibles, the things we perceive incidentally by way of each sense — for example motion, rest, shape, magnitude, number, unity. For we perceive all of these by motion; for example, we perceive magnitude by motion. Hence also shape, for shape is a kind of magnitude. And what is at rest we perceive by its not moving; and number by the negation of the continuous, and by the special perceptibles, for each sense perceives one thing. So it is clear that it is impossible for there to be a special sense for any of these, for example for motion; for then it would be as it now is when we perceive sweetness by sight. And this is because we happen to have perception of both qualities, by which we also recognize them when they coincide.
3| whereas otherwise we could not perceive them at all except incidentally, as we perceive the son of Cleon not because he is the son of Cleon but because he is white, and it is incidental to this white thing that it is the son of Cleon. But of the common perceptibles we already have a common perception, and not incidentally; so it is not a special perception. For otherwise we could perceive them in no other way than the way stated, by which we see the son of Cleon. But the senses perceive one another's special objects incidentally, not insofar as they are the same senses, but insofar as they form a unity, whenever the perception occurs at the same time upon the same object — for example, that bile is bitter and yellow; for it is surely not the business of a different sense to say that the two are one; hence too one is deceived, and if a thing is yellow, one supposes it to be bile. One might inquire for what purpose we have several senses and not one alone. Is it so that the accompanying and common attributes — such as motion, magnitude, and number — are less likely to escape notice? For if sight alone existed, and it were a sight only of white, these attributes would escape notice more, and everything would seem to be the same, on account of color and magnitude always accompanying one another. But as it is, since the common attributes also occur in a different perceptible, this makes it clear that each of them is something distinct.
4| Since we perceive that we see and hear, it is necessary either that we perceive that we see by sight, or by some other sense. But then the same sense will be of sight and of the underlying color. So that either there will be two senses of the same thing, or the same sense will be of itself. Further, if the sense of sight itself were different from sight, either it will go on to infinity or some sense will be of itself. So this must be granted in the case of the first sense. But there is a difficulty here: if perceiving by sight is seeing, and what is seen is color or that which has color, then if one is to see the thing that sees, the thing that sees will itself have color to begin with. It is clear, then, that perceiving by sight is not a single thing; for even when we are not seeing, we discriminate darkness and light by sight, though not in the same way. Further, even the thing that sees is in a way colored; for the sense-organ is receptive of the perceptible object without its matter, in each case. Hence even when the perceptible objects have departed, perceptions and images remain present in the sense-organs. And the actuality of the perceptible object and that of the perception are one and the same, though their being is not the same for both; I mean, for example, sound in actuality and hearing in actuality.
5| for it is possible to have hearing and not be hearing, and what has sound is not always sounding. But whenever what is capable of hearing is in actuality exercising it, and what is capable of sounding is sounding, then hearing in actuality and sound in actuality occur together, of which one might call the one hearing-in-act and the other sounding. If motion, acting, and being affected are all in the thing acted upon, then it is necessary that both sound and hearing in actuality be in that which has them in potentiality; for the actuality of the agent and mover comes to be in the thing affected. Hence it is not necessary that the mover itself be moved. Now the actuality of what is capable of producing sound is sound or sounding, and the actuality of what is capable of hearing is hearing or audition; for hearing is twofold, and sound is twofold. The same account holds for the other senses and perceptibles as well. For just as acting and being acted upon are in the thing acted upon and not in the agent, so too the actuality of the perceptible and that of the perceptive faculty are in the perceptive faculty. But in some cases both have been given names, such as sounding and hearing, while in others one of the two is nameless;
6| for the actuality of sight is called seeing, but that of color has no name, and the actuality of what tastes is called tasting, but that of flavor has no name. And since the actuality of the perceptible and that of the perceptive faculty are one, though their being is different, it is necessary that hearing and sound, spoken of in this way, perish and are preserved together, and likewise flavor and taste, and the others in the same way; but this is not necessary for what is spoken of in terms of potentiality. The earlier natural philosophers did not put this well, thinking that nothing is white or black without sight, nor is there any flavor without taste. For in one sense they spoke correctly, but in another sense not correctly; for since both perception and the perceptible are spoken of in two ways, some in terms of potentiality and others in terms of actuality, what they said holds true of the latter, but does not hold of the former. But they spoke without qualification about things that are not said without qualification. And if a concord is a kind of sound, and voice and hearing are in a way one and the same and in a way not the same, and a concord is a ratio, then hearing too must be some sort of ratio. And this is why anything excessive destroys hearing, both the high-pitched and the low-pitched;
7| Similarly too, taste suffers from excess in flavors, and sight in colors by what is exceedingly bright or dark, and smell by a strong odor, whether sweet or bitter — since perception is a kind of ratio. That is why things are pleasant when they are brought into the ratio pure and unmixed — for example the sharp, the sweet, or the salty; for then they are pleasant. But in general the mixed is more a concord than the sharp or the low note. In touch, it is the heating or the cooling; the perception is the ratio; and when these are in excess they cause pain or destroy the sense. Each sense, then, is of its underlying perceptible object, existing in the sense organ insofar as it is a sense organ, and it discriminates the differentiae of its underlying perceptible object — sight for example discriminates white and black, taste sweet and bitter. And the same holds for the other senses. But since we also discriminate white and sweet and each of the perceptible objects in relation to one another, we perceive by something that they differ. This must be by perception, then, since they are perceptible objects. This also makes clear that the flesh is not the ultimate sense organ; for what discriminates would necessarily have to discriminate by being in direct contact with the object. Nor can separate faculties discriminate that the sweet is different from the white; rather, both must be evident to one and the same thing.
8| For in this way, even if I perceived the one and you the other, it would be clear only that they are different from each other, not that one thing discriminates the difference. It must be one thing that says they are different; for the sweet is different from the white. So it is the same thing that says this. Hence as it says, so it also thinks and perceives. That it is not possible for separate things to discriminate what is separate, then, is clear; and that it cannot happen in separate time either is clear from the following. For just as it is the same thing that says the good and the bad are different, so too, when it says that one of the two is different, it also says the other is different, and does so at the same time — and this "when" is not incidental. I mean, for example: when I say now that they are different, I do not merely mean that they are different now. Rather it says this in this way: both now, and that it is now; so it is at once. Hence it acts undivided, and in undivided time. But is it not impossible for the same thing to be moved by contrary motions at once, insofar as it is undivided and in undivided time? For if the sweet moves perception or thought in one way, and the bitter in the contrary way, and the white in yet another way — is the discriminating {faculty}, then, at once undivided and inseparable in number, but separate in being? In one way it is as the divisible that perceives things that have been divided, and in another way it is insofar as it is undivided —
9| for in being it is divisible, but in place and in number it is undivided. Or is this not possible? In potentiality, one undivided thing can hold both contraries at once; not so in actuality, where, once actualized, it splits, and nothing can be black and white together. So it does not undergo the contrary forms themselves either, if perception and thought are of this kind; rather, just as what some call a point is, in one respect, one, and in another, two, so too it is divisible in this same respect. Insofar, then, as it is undivided, the discriminating {faculty} is one and acts at once; but insofar as it is divisible, it uses the same point twice at once. Insofar, then, as it uses {the point} as two, it discriminates two things with the limit, treating them as separate as though they belonged to separate things; but insofar as it is one, it discriminates with one thing and at once. Concerning the principle, then, by which we say the animal is capable of perception, let this determination stand. Since it is chiefly by two differentiae that people define the soul — by motion in respect of place, and by thinking, discriminating, and perceiving — and since thinking and being practically wise are also thought to be a kind of perceiving (for in both of these the soul discriminates something and comes to know one of the things that are), the ancients indeed say that being practically wise and perceiving are the same, as Empedocles too has said: "for wisdom grows in men in accordance with what is present before them," and elsewhere
10| "from which it is that thinking is always presented to them as something different." And Homer's line means the same thing: "for such is the mind of men." For all these thinkers suppose that thinking is bodily, like perceiving, and that both perceiving and being practically wise occur by like knowing like, as we determined in our opening discussions. And yet they ought to have spoken at the same time about being deceived as well; for this is more proper to animals, and the soul spends more of its time in this condition. So it is necessary either, as some say, that all appearances are true, or that error is contact with the unlike; for this is the contrary of like being known by like. But error and knowledge of contraries are also thought to be the same. That perceiving and being practically wise are not the same, then, is clear; for all animals share in the one, but few in the other. Nor is thinking either the same as perceiving — thinking, in which there is the correct and the incorrect, the correct being practical wisdom, knowledge, and true opinion, and the incorrect being the contraries of these; this too is not the same as perceiving. For perception of the proper objects of each sense is always true, and belongs to all animals, whereas it is possible to think falsely too, and thinking belongs to nothing that does not also have reason.
11| For imagination is different both from perception and from thought; it does not occur without perception, and without it there is no supposition. That thinking and supposition are not the same is clear. For this affection of imagining is up to us, whenever we wish — it is possible to set something before our eyes, as those do who arrange things in mnemonic systems and construct images — but forming opinion is not up to us, since we must either be in error or speak truly. Further, whenever we form the opinion that something is terrible or frightening, we are immediately affected accordingly, and likewise if it is something reassuring; but with imagination we are in the same condition as those who look at terrible or reassuring things in a painting. And there are also differentiae within supposition itself — knowledge, opinion, practical wisdom, and their contraries — but discussion of their difference belongs elsewhere. As for thinking, since it is different from perceiving, and of thinking one part seems to be imagination and the other supposition, we must first determine the nature of imagination, and speak of the other in the same way afterward. If, then, imagination is that in virtue of which we say some appearance occurs in us — and not what we say by way of metaphor — is it one of those capacities or states by which we discriminate and are either right or in error?
12| Such are perception, opinion, knowledge, and intellect. That it is not perception is clear from the following. For perception is either a capacity or an activity — for example sight as a capacity and seeing as an activity — but something appears to us even when neither of these is present, as in dreams. Again, perception is always present, but imagination is not. And if it were the same as the activity of perceiving, it would be possible for imagination to belong to all beasts; but this does not seem to be so — for example, in the ant, the bee, or the grub. Again, perceptions are always true, while imaginings are, for the most part, false. Further, when we are exercising perception accurately with regard to the perceptible object, we do not say that this appears to us to be a man; rather, it is when we do not perceive clearly that what appears is either true or false. And, as we said before, visions appear even to those whose eyes are shut. But neither, on the other hand, will it be any of those states that are always true, such as knowledge or intellect; for imagination can also be false. It remains, then, to see whether it is opinion; for opinion can be both true and false. But conviction follows upon opinion (for it is not possible for one who holds an opinion not to believe what he opines), whereas none of the beasts has conviction, though many have imagination. Further, conviction follows every opinion, being persuaded follows conviction, and being persuaded requires reason —
13| Some beasts have imagination but not reason. It is clear, then, both for this reason and because it is evident that opinion is not of some other object than the one perception is also of, that imagination could not be opinion together with perception, nor opinion through perception, nor a combination of opinion and perception. I mean: on that view, imagination would be a combination formed out of the opinion of white and the perception of white; for it is surely not formed out of the opinion of the good and the perception of white. Appearing, then, would be holding the very opinion that one perceives, and not accidentally. But false appearances also occur, concerning things about which one holds a true belief at the very same time — for example, the sun appears a foot across, but it is believed to be larger than the inhabited world. It follows, then, either that one has cast off one's own true opinion, the one held, although the fact remains unchanged, without having forgotten it or been persuaded otherwise, or, if one still holds it, the same opinion must be both true and false. But it would only become false when the fact changed and one failed to notice. Imagination, then, is neither any single one of these nor composed out of them. But since, when a given thing is moved, something else is moved by it, and imagination seems to be a kind of motion and not to occur without perception, but only for beings that perceive and about things of which there is perception; and since it is possible for a motion to arise from the actuality of perception, and this motion must be similar to the perception — this motion would be one that neither can occur without perception nor can belong to beings that do not perceive, and the thing that has it can, in virtue of it, both do and undergo many things, and can be both true and false.
14| This happens for the following reasons. Perception of the special objects is true, or has the least amount of falsehood in it. Second is perception of the fact that these are accidental attributes of something; and here it is already possible to be deceived: for it is not mistaken that a thing is white, but whether this white thing is this thing or another, there it is mistaken. Third is perception of the common attributes and of what follows upon the accidents to which the special objects belong; I mean, for example, motion and magnitude, which are accidental to perceptible things, and concerning which it is now above all possible to be deceived by perception. The motion produced by the actuality of perception will differ according to which of these three kinds of perception it comes from. The first is true while the perception is present; the other two may be false whether the perception is present or absent, and especially when the perceptible object is far away. If, then, what has been said belongs to nothing but imagination, and this is what has just been described, imagination would be a motion produced by perception when perception is in actuality. And since sight is perception most of all, imagination has taken its name from light, because without light it is impossible to see. And because images persist and resemble perceptions, animals do many things in accordance with them — some because they lack intellect, as the beasts do, others because their intellect is sometimes clouded over by emotion, or by illness, or by sleep, as with human beings.
15| Concerning imagination, then — what it is and why it exists — let this much be said. Concerning the part of the soul by which the soul knows and thinks, whether it is separable or not separable in magnitude but only in account, we must examine what differentia it has, and how thinking ever comes about. If, then, thinking is like perceiving, it would be either a kind of being-acted-on by the object of thought, or something else of that sort. It must, then, be unaffected, yet receptive of the form, and potentially such as the form is, though not actually that form, and it must stand to the objects of thought as the perceptive part stands to the objects of perception. It must, therefore, since it thinks all things, be unmixed, as Anaxagoras says, so that it may rule — that is, so that it may know. For anything foreign appearing alongside it would hinder and obstruct it, so that it has no nature of its own at all, except this one: that it is potential. The part of the soul called intellect, then (I mean the intellect by which the soul reasons discursively and forms judgments), is actually none of the things that are, before it thinks. For this reason it is not reasonable that it should be mixed with the body either; for then it would become qualified in some way, cold or hot, or would even have some organ, as the perceptive part does; but as it is, it is nothing of the kind.
16| And those who say the soul is the place of forms speak well, except that it is not the whole soul but only the intellective part, and the forms are present in it not in realization but in potentiality. That the impassivity of the perceptive part and that of the intellective part are not alike is clear from the sense organs and from perception. For perception is unable to perceive after being affected by an intensely perceptible object — for instance, sound after very loud sounds — nor, after strong colors or odors, is it able either to see or to smell. But the intellect, when it has thought something highly intelligible, thinks the lesser things no less well — indeed, even better. For the perceptive part does not exist apart from the body, whereas the intellect is separable. But when the intellect has become each of its objects in the way that a person is said to be knowledgeable in actuality (which happens when he is able to exercise this knowledge on his own), it is then too, in a way, still in potentiality, though not in the same way as before he learned or discovered it; and then it is also able to think itself. Now, since magnitude and being-a-magnitude are different, and water and being-water are different — and so too in many other cases, though not in all, for in some cases being-flesh and flesh are the same —
17| one judges being-flesh and flesh either by something different, or by something differently disposed; for flesh does not exist apart from matter, but is like the snub, a this in a this. With the perceptive part, then, one judges the hot and the cold, and the things of which flesh is a certain ratio; but with something else — either separate, or related to the perceptive part as a bent line is to itself when it has been straightened out — one judges being-flesh. Again, among things that exist by abstraction, the straight is like the snub, for it exists together with something continuous; but its essence — if being-straight and the straight-in-something-else are different — is judged by something else; let this be twoness. One judges, then, by something different, or by something differently disposed. And so, in general, as things are separable from matter, so too are the corresponding operations of the intellect. One might raise the difficulty: if the intellect is simple and unaffected and has nothing in common with anything, as Anaxagoras says, how will it think, if thinking is a kind of being-acted-on? For it is insofar as something is common to both that the one seems to act and the other to be acted on. Again, there is the question whether it is itself an object of thought. For either intellect will belong to other things too, if it is not itself thinkable in virtue of something else, while the intelligible is one in form, or else it will have something mixed into it, which makes it, like other things, an object of thought.
18| Or rather, being-acted-on in virtue of something common has already been distinguished earlier: that the intellect is, in a way, potentially the objects of thought, but actually none of them, before it thinks. It must be as with a writing tablet on which nothing actually written yet exists — which is exactly what happens in the case of the intellect. And it is itself an object of thought, just as its objects are. For in the case of things without matter, that which thinks and that which is thought are the same; for theoretical knowledge and its object, known in this way, are the same — but the cause of its not always thinking must be examined. But in things that have matter, each of the objects of thought is present only potentially. So intellect will not belong to them (for the intellect is the potentiality of such things apart from their matter), but the intelligible will belong to intellect.
19| Since, just as in all of nature there is something that is matter for each kind (and this is what is potentially all the things of that kind), and something else that is the cause and is productive, by producing all of them, in the way that craft is related to its matter, these same differentiae must also be present in the soul. And there is an intellect of this sort by becoming all things, and another by producing all things, as a kind of state, like light; for in a way light too makes colors that are potentially colors into colors in actuality. And this intellect is separable, unaffected, and unmixed, being in its substance an actuality. For the agent is always more honorable than the patient, and the principle more honorable than the matter. Actual knowledge is the same as its object; but potential knowledge is prior in time in the individual, though not at all prior in time taken generally; but it is not the case that it thinks at one time and does not think at another. Once separated it is only just what it is, and this alone is immortal and eternal. We do not remember, because this part is unaffected, while the passive intellect is perishable, and without this nothing thinks.
20| The thinking of indivisibles, then, occurs among things about which there is no falsehood; but among things where there is also falsehood and truth, there is already a certain combination of thoughts as though they were one, the way Empedocles said that where many necks sprang up without heads, and then these were combined by love. So too these separated things are combined, for instance the incommensurable and the diagonal. But if the thinking concerns things coming to be or things that will be, it thinks by additionally thinking the time and combining it in. For falsehood is always in a combination; for even if one says the white is not white, one has combined not-white with it. It is also possible to call all of these a division. But at any rate there is not only falsehood or truth in saying that Cleon is white, but also in saying that he was or will be. And that which makes a unity of this — this is the intellect in each case. And since the indivisible is spoken of in two ways, either potentially or actually, nothing prevents the mind from thinking the indivisible when it thinks a length; for it is indivisible in actuality, and in an indivisible time; for time is divisible and indivisible in the same way as length is. It is not possible, then, to say what the mind is thinking in each half; for it is not there, unless it has been divided, but only potentially. But thinking each of the halves separately, it divides the time as well, at the same time —
21| — and then they are as it were two lengths. But if it thinks them as arising out of both together, it thinks also in the time covering both. And whatever is indivisible not in quantity but in form, the mind thinks in an indivisible time and with an indivisible part of the soul; but this is accidental, and not insofar as those things are divisible by which it thinks and in which time it thinks, but insofar as they are indivisible; for even in these there is something indivisible, though perhaps not separable, which makes the time and the length one. And this holds alike in everything continuous, both time and length. The point, and every division, and whatever is indivisible in this way, is made evident the way a privation is. And the argument is similar for the other cases too, for instance how one comes to know evil, or black; for one knows it in a way by means of its contrary. And that which knows must be potentially the contrary and must have it present within itself. But if for something among the causes there is no contrary, it knows itself, and is in actuality and separable. And an assertion is something said of something, as an affirmation is, and every affirmation is true or false; but intellect is not so in every case — the intellect that grasps what a thing is, in respect of its essence, is true, and it is not something said of something —
22| — but rather, just as sight is true of its proper object, while whether the white thing is a man or not is not always true, so it is with things that exist without matter. Actual knowledge is the same as its object. Potential knowledge is prior in time in the individual, but taken generally it is not prior in time at all; for everything that comes to be comes from something that already exists in full actuality. It is evident that the perceptible object, out of what is perceptive existing potentially, produces it as actual; for the perceptive faculty is not acted upon nor altered. Hence this is a different kind of motion; for motion was the actuality of what is incomplete, while actuality without qualification — that of what has been completed — is a different thing. Perceiving, then, is like bare asserting and thinking; and when the object is pleasant or painful, the soul, as it were affirming or denying, pursues or avoids it; and to feel pleasure or pain is to be active with the perceptive mean toward the good or the bad, as such. And avoidance and desire, when actual, are this very activity, and the faculty of desire and the faculty of avoidance are not different — not from each other, nor from the perceptive faculty; but their being is different. For the thinking soul, images serve the function that perceptions do. And when it affirms or denies something as good or bad, it avoids or pursues it. Hence the soul never thinks without an image, just as the air affects the pupil in one way, and the pupil itself is affected differently, and hearing likewise —
23| — but the last organ is one, and there is a single mean for it, though its being is manifold. By what faculty it discriminates how sweet and hot differ has been stated before, but it should be stated here too. For there is some one thing, and it functions as a boundary. And these are one by analogy, and by the ratio each has to the other, as those qualities have to one another; for what difference is there between asking how it discriminates things of the same kind and how it discriminates opposites, for instance white and black? Let A, the white, be to B, the black, as C is to D, so that they also alternate. If then C and D belong to one thing, that thing will be in the same condition as A and B — the same and one, though their being is not the same, and likewise for the other pair. And the same argument holds if A were the sweet and B the white. The intellective faculty, then, thinks the forms in images, and just as in those images what is to be pursued and avoided is marked out for it, so also, outside of perception, when it is occupied with images, it is moved — for example, perceiving by the common sense that the beacon-fire is fire, it recognizes, on seeing it move, that it signals an enemy.
24| At times, by means of the images or thoughts within the soul, as though seeing them, it calculates and deliberates about future things in relation to present ones; and when it says that the pleasant or painful is there, then here it avoids or pursues it, and in general acts. And even apart from action, the true and the false are in the same genus as the good and the bad; but they differ in that the one is unqualified and the other is qualified by relation to something. It thinks the things spoken of by abstraction the way one would think the snub: as snub, it is not thought apart, but as concave, if someone were thinking it in actuality, he would think it apart from the flesh in which the concavity lies. So too it thinks mathematical objects, which are not separate, as separate, whenever it thinks them. And in general, intellect in actuality is the things it thinks. But whether it is possible for it, while itself not separate from magnitude, to think any of the things that are separate, or not, must be examined later.
25| Now that we have summed up what has been said about the soul, let us say again that the soul is, in a way, all the things that are. For the things that are, are either perceptible or intelligible, and knowledge is, in a way, the things known, while perception is the things perceived; in what way this is so, we must inquire. Knowledge and perception, then, are divided to match the things: the potential kind of knowledge and perception to the potential things, the actual kind to the actual things. The perceptive and the knowing part of the soul are potentially these things: the one the knowable, the other the perceptible. And they must be either the things themselves or their forms. They are not the things themselves, of course, for it is not the stone that is in the soul, but its form; so that the soul is like the hand. For the hand too is a tool of tools, and intellect is a form of forms, and perception a form of perceptible things. And since no thing exists, so it seems, separately apart from the magnitudes that are perceptible, it is in the perceptible forms that the intelligible objects exist — both the things spoken of by abstraction, and whatever states and affections belong to perceptible things. And this is why someone who perceives nothing could learn or understand nothing; and whenever one is contemplating, one must at the same time be contemplating some image, for images are like perceptions, except without matter. And imagination is different from affirmation and denial; for truth and falsehood are a combination of thoughts. But how will the first thoughts differ from being images? Or rather, the other thoughts too are not images, but not without images.
26| Now since the soul of animals is marked off by two capacities — by the discriminative capacity, which is the work of thought and of perception, and further by the capacity to produce motion in respect of place — let this much stand as our determination about perception and intellect, and let us consider, concerning the moving element, whatever it may be of the soul, whether it is some one part of it, separate either in magnitude or in account, or the whole soul, and, if it is some part, whether it is something peculiar besides those usually spoken of and already mentioned, or one of these. There is an immediate difficulty as to how we ought to speak of parts of the soul, and how many there are. For in a way they appear infinite, and not only those which some mark off in distinguishing them — the calculative, the spirited, and the appetitive, or, as others put it, the rational and the irrational; for according to the differentiae by which they separate these off, other parts too will appear, having a greater distinction than these — the parts about which indeed something has just now been said: the nutritive, which belongs also to plants and to all animals, and the perceptive, which one could not easily class either as irrational or as possessing reason. Further there is the imaginative, which, while being in its being different from all of these, is, in relation to some one of them, the same or different — and this presents much difficulty, if one is to posit separated parts of the soul.
27| And besides these there is the desiderative, which would seem to be different from all the others both in account and in capacity. And it is indeed absurd to tear this apart from the others; for wish arises in the calculative part, and appetite and spirit in the irrational part; and if the soul is threefold, there will be desire in each of the three. And so, concerning the very matter our discussion is now engaged with — what is it that moves the animal in respect of place? For the motion in respect of growth and decay, which belongs to all things, would seem to be moved by that which is present in all — the generative and nutritive capacity; concerning breathing in and breathing out, and sleep and waking, we must inquire later, for these too present much difficulty. But concerning motion in respect of place, we must consider what it is that moves the animal in its progressive motion. That it is not the nutritive capacity, then, is clear; for this motion is always for the sake of something, and it involves either imagination or desire, for nothing moves that does not either desire or avoid something, except by force. Further, even plants would have been capable of motion, and would have had some organic part for this motion, if this capacity sufficed. And likewise it is not the perceptive capacity either; for there are many animals which have perception but are stationary and motionless through their whole existence.
28| If, then, nature does nothing in vain, and leaves out nothing that is necessary, except in the case of the maimed and the incomplete — and such animals as these are complete and not maimed, a sign of which is that they are capable of generation, and have a prime of life and a decline — then they would also have had the organic parts for progressive motion, had this capacity sufficed to produce it. But surely it is not the calculative faculty either, nor what is called intellect, that is the mover; for the theoretical intellect thinks nothing that is practical, and says nothing about what is to be avoided or pursued, whereas motion belongs to something that is avoiding or pursuing something. But not even when the intellect is contemplating something of this sort does it thereby command us to avoid or pursue it — for instance, one often has in mind something fearful or pleasant, without its commanding one to be afraid; instead the heart is moved, or, if the thing is pleasant, some other part. Further, even when the intellect gives an order, and thought bids us avoid or pursue something, we are not moved, but act according to appetite — as does the person lacking self-control. And in general we observe that a person who possesses the medical art does not thereby heal, as though there were something else in control of acting in accordance with the knowledge, and not the knowledge itself. But surely desire, too, is not in control of this motion;
29| for the self-controlled, though they have desire and appetite, do not do the things for which they have the desire, but follow the intellect. There appear, at any rate, to be these two things that produce motion: either desire or intellect, if one is to posit imagination as a kind of thinking; for people follow their imaginations in many cases contrary to knowledge, and in the other animals there is neither thought nor calculation, but imagination. Both of these, then, are productive of motion in respect of place: intellect and desire. And the intellect in question is the one that calculates for the sake of something, that is, the practical intellect; it differs from the theoretical intellect in its end. And desire too is always for the sake of something; for that which is the object of desire is the starting point of the practical intellect, and the last term is the starting point of action. So it is reasonable that these two should appear as the movers, desire and practical thought; for the object of desire moves, and it is on this account that thought moves — because the object of desire is its starting point. And imagination too, when it produces motion, does not produce motion without desire. There is, then, some one thing that moves, the object of desire. For if two things moved, intellect and desire, they would move in virtue of some common form. But as it is, intellect plainly does not move without desire — for wish is a form of desire; and whenever one is moved according to calculation, one is also moved according to wish. But desire moves also contrary to calculation;
30| for appetite too is a kind of desire. Now intellect is always right; but desire, and imagination too, may be either right or not right. This is why it is always the object of desire that moves, but this object is either the good or the apparent good — not every good, but the practical good. And the practical good is that which admits of being otherwise. That it is this capacity of the soul, then, that moves, the one called desire, is evident. But for those who divide the parts of the soul, if they divide and separate them according to their capacities, a very great number of parts result — nutritive, perceptive, thinking, deliberative, and further desiderative; for these differ from one another more than the appetitive and the spirited do. But since desires arise contrary to one another, and this occurs when reason and appetite are contrary, which happens in creatures that have a perception of time (for intellect, on account of the future, bids us pull against appetite, while appetite bids us follow on account of the present; for what is present appears pleasant both without qualification and good without qualification, because one does not see the future) — in form, then, that which moves, the desiderative, in so far as it is desiderative, would be one, and first of all is the object of desire (for this moves without being moved, by being thought or imagined), but in number the movers are more than one.
31| Since there are three things, one the mover, second that by which it moves, third the thing moved; and the mover is twofold, on the one hand the unmoved, on the other that which both moves and is moved; and the unmoved is the practical good, while that which both moves and is moved is the desiring part (for what is moved is moved insofar as it desires, and desire, insofar as it is actual, is a kind of motion), and the thing moved is the animal; and the organ by which desire moves is already something bodily, so that it must be studied among the functions common to body and soul. For now, to speak in summary, that which moves organically is where starting point and end point are the same, as with a hinge-joint; for there the convex and the concave, the one is end point, the other starting point, and so the one is at rest and the other moves, being different in account but inseparable in magnitude, for all things move by pushing and pulling. So there must be something that stays still, as at the center of a circle, and it is from there that the motion begins. In general, then, as has been said, insofar as the animal is a thing capable of desire, in that respect it is capable of moving itself; and it is not capable of desire without imagination, and every imagination is either calculative or perceptual. In this latter kind the other animals too share.
32| We must also consider, concerning the incomplete animals, those which have only touch as a sense, what the mover is in them, whether it is possible for imagination to be present in them, or not, and appetite. For pain and pleasure evidently are present in them. And if these are present, then appetite too must be present of necessity. But how could imagination be present? Well, just as these animals also move indeterminately, so too these are present in them, but present indeterminately. Now perceptual imagination, as has been said, is present in the other animals as well, but deliberative imagination is present only in the calculative animals; for whether one shall do this or that is already the work of calculation, and one must measure by a single standard, for one pursues the greater good. So it is possible to make one image out of several images. And this is the reason why such animals are thought not to have opinion, because they do not have the imagination that comes from reasoning, whereas this deliberative kind does have that other kind within it. That is why desire, taken alone, does not have the deliberative faculty. And sometimes desire prevails and moves the wish, and sometimes the wish moves desire, like one ball striking another, desire moving desire, when there is lack of self-control. But by nature the higher is always more sovereign and does the moving, so that already three kinds of motion are moving. And the part concerned with knowledge does not move, but stays at rest. Since the one supposition and account is universal, while the other concerns the particular case (for the one says that a person of such a kind ought to do such a thing, while the other says that this particular thing here now is of such a kind, and I am a person of such a kind), it is already this latter opinion that moves, not the universal one. Or rather both move, but the one does so while remaining more at rest, the other not.
33| It is necessary, then, that everything which lives and has soul, from birth to destruction, possess the nutritive soul; for what has come into being must have growth, a prime, and decline, and these are impossible without nourishment; so the nutritive capacity must necessarily be present in all things that grow and decline. But perception need not be present in all living things; for it is not possible for those whose body is simple to have touch, and yet it is not possible for anything to be an animal without touch, nor for anything not receptive of forms apart from matter. And the animal must necessarily have perception, if nature does nothing in vain. For all things that exist by nature exist for the sake of something, or else they will be by-products of things that exist for the sake of something. If, then, any body capable of forward motion did not have perception, it would perish and would not arrive at its end, which is the work of nature; for how will it be nourished? For stationary things have the source from which they naturally grow already at hand; but it is not possible for a body to have soul and a discriminating intellect and yet not have perception, if it is not stationary but comes into being. But neither is it possible for it to be ungenerated; for why would it have this? Either it would be better for the soul or for the body.
34| But as things stand, it is better for neither: the soul will not think any the more for it, and the body will be no better off on that account. So nothing that has soul and is not stationary is without perception. But then, if it has perception, its body must necessarily be either simple or mixed. But it cannot be simple, for it will not have touch, and it is necessary for it to have this. This is clear from the following. Since the animal is an ensouled body, and every body is tangible, and the tangible is what is perceptible by touch, the animal's body must necessarily be capable of touch too, if the animal is to survive. For the other senses perceive through other media, for example smell, sight, hearing; but a thing that touches, if it does not have this sense, will not be able to avoid some things and grasp others. And if this is so, it will be impossible for the animal to survive. That is why taste too is a kind of touch; for it is a sense of food, and food is the tangible body. But sound and color and smell do not nourish, nor do they produce either growth or decline. So taste too must necessarily be a kind of touch, because it is a perception of what is tangible and nourishing. These senses, then, are necessary for the animal, and it is plain that it is not possible for an animal to exist without touch.
35| The other senses exist for the sake of well-being, and belong already not to any chance kind of animal but to certain kinds, for example they must be present in the kind capable of forward motion; for if it is to survive, it must perceive not only by touching but also from a distance. And this would come about if it were capable of perceiving through an intervening medium, in that the medium is affected and moved by the perceptible object, and the animal itself is affected by the medium. For just as that which causes motion in respect of place produces its effect up to the point of causing change, and what has pushed makes something else push in turn, and the motion occurs through an intermediate, and indeed the first mover pushes without being pushed, while the last thing is only pushed and does not push, and the middle thing does both, and there are many middle things, so it is too in the case of alteration, except that the thing alters while remaining in the same place, as if one were to dip something into wax: the motion goes only as far as the point where the dipping occurred; a stone is affected not at all, but water is affected to a considerable distance. Air is affected over the greatest distance, and both acts and is acted upon, provided it remains still and is one continuous mass. That is why, regarding reflection too, it is better to say not that the sight goes out and is bent back, but that the air is affected by the shape and color, for as far as it remains one continuous mass.
36| And on a smooth surface it is one continuous mass; that is why this in turn moves the sight, just as if the mark made in the wax were transmitted all the way to the boundary. That it is not possible for the animal's body to be simple is clear, I mean, for example, made of fire or of air. For without touch it is not possible to have any other sense; for every ensouled body is capable of touch, as has been said. As for the other elements apart from earth, they might become organs of sense, but all of them produce perception by perceiving through something else and through media. But touch consists in the animal's own parts touching the object itself, which is why it has this very name. And yet the other sense organs too perceive by a kind of touch, but through something else, whereas this one alone seems to perceive through itself. So none of the other elements of that kind could be the animal's body. Nor indeed could it be earthy. For touch is, as it were, a mean among all tangible things, and the sense organ is receptive not only of the differentiae of earth, but also of hot and cold and all the other tangible qualities. And this is why we do not perceive with our bones and hair and parts of that sort, because they are of earth. And plants, for this same reason, have no perception at all, because they are of earth; and without touch it is not possible for any other sense to be present, and this sense organ is neither of earth nor of any other single one of the elements.
37| It is clear, then, that animals necessarily die when they are deprived of this sense alone, touch; for it is not possible for a non-animal to have this sense, nor is it necessary for an animal, once it is an animal, to have any sense besides this one. And for this reason the other objects of sense do not, by their excesses, destroy the animal — for example color, sound, and smell — but only the sense-organs, unless accidentally, as when a push and a blow occur together with the sound, or when other things are set in motion by sights and smells and these destroy by way of touch. And flavor too, insofar as it happens at the same time to be tangible, destroys in that respect. But the excess of tangible qualities — of hot and cold and hard, for example — destroys the animal; for the excess of any object of sense destroys the sense-organ, so that the tangible destroys touch as well, and living is defined by this; for it has been shown that it is impossible for an animal to exist without touch. That is why the excess of tangible qualities destroys not only the sense-organ but the animal too, because touch is the only sense it necessarily has. The other senses the animal has, as has been said, not for the sake of being but for the sake of being well: sight, for instance, since it lives in air or water, so that it may see, and in general since it lives in something transparent; and taste, on account of the pleasant and the painful, so that it may perceive what is in its food, and desire it, and be moved; and hearing, so that something may be signified to it; and the tongue, so that it may signify something to another.